A Superconducting Quantum Interference Device (SQUID) is a highly sensitive magnetometer used to measure extremely weak magnetic fields. It operates based on the principles of superconductivity and quantum interference, utilizing a loop of superconducting material with one or two Josephson junctions. These junctions allow for the flow of supercurrents, which can interfere with each other, enabling precise measurements of magnetic flux. SQUIDs are widely used in various fields, including medical imaging (like MRI), geophysics, and particle physics. Their ability to detect minute changes in magnetic fields makes them valuable for research and practical applications, such as studying brain activity or exploring geological formations.